The present invention relates to an electric circuit for regulating a pulsating current by an inductor, in particular the coil of an electromagnetic valve, the inductance being connected in series with a semiconductor switch in parallel to a free-running diode, and a desired-value voltage being further adapted to be fed to a controller the output of which is connected via a pulse-width modulator to a control input of the semiconductor switch. By way of example, the circuit is particularly useful in the operation of an electromagnetic valve of a fuel-injection system for an internal combustion engine.
For regulating a pulsating current by an inductor, as accurate as possible a detection of the current is necessary. In the known circuits a current flows through a semiconductor switch and the inductor in a first part of a period of pulsation of the current. The semiconductor switch is nonconductive in a second part of the period. The magnetic energy stored in the inductor, however, produces a further flow of current through a so-called "free-running circuit" which consists of the inductor and a parallel-connected free-running diode. An exact measurement of the total current can actually be effected only in the feed lines of the inductance, which, however, is frequently not possible based on considerations of circuit construction technique.